European Journal of Solid State and Inorganic Chemistry最新文献

The emission spectra of both single crystals and polycrystalline samples of Ca₂PO₄Cl “doped” with VO₄³⁻ have been measured at several temperatures from 10 K to room temperature. In both a wide emission band has been observed within the range 16000–28000 cm⁻¹. This band shows two components, which behave differently with temperature. The deconvolution of the decay curves, expressed in terms of a linear combination of exponentials, requires three exponentials below 250 K. The relative lifetimes are 3700 μs, 1800 μs and 250 μs at 10 K. The emission wide band is assigned to a triplet → singlet transition connected to a transfer of an electron from a molecular orbital mainly localized on one oxygen atom (2pπ type) to a molecular orbital mainly localized on the vanadium atom (d_e, or d_i2 type). The lifetimes of the single crystal and of the polycrystalline samples are rather close. However there is evidence of a somewhat different behaviour of the two kinds of samples with temperature.

A new semi-continuous process has been developed for the synthesis of Cr₂O₃ powders starting with Cr(III) acetylacetonate or acetate hydroxide dissolved in methanol. The precursor is first decomposed in the solvent under supercritical state (T = 325 to 450 °C, P = 10 MPa) and the formed solid is dried under either nitrogen or air flow. For various reaction temperatures and drying conditions, nanometric particles of pure amorphous or crystalline Cr₂O₃ powders are obtained with surface area between 350 and 30 m².g⁻¹ according to their crystallization state.

Synthesis and complete structural characterization by X-ray diffraction, DTA, GTA and IR are given for a new cyclohexaphosphate: (1,6-NH₃C₆H₁₂NH₃)₂ (1-NH₃C₁₀H₇)₂P₆O₁₈.2H₂O. This compound is monoclinic P2₁/c with the following unit-cell parameters: a = 11.861(2)Å, b = 10.104(1)Å, c = 19.664(6)Å, β = 96.44(2)°, and Z = 2. The crystal structure has been solved and refined to R = 0.033 using 3928 independent reflections. The atomic arrangement can be described as layer organisation. Layers built by P₆O₁₈ ring anions and water molecules spread in the plans (100). Between these layers are located the organic groups which form hydrogen bonds with oxygen atoms of P₆O₁₈ rings and water molecules. Geometrical characteristics of hydrogen bonds are described. The reported IR study is supported by a delaited theoretical group analysis applied to P₆O₁₈ with D_6h ideal local symmetry.

This paper reports the study of manganese substituted barium fluoroapatite Ba₁₀(P_1−xMn_xO₄)₆F₂ with 0 ≤ × ≤ 0.20. X-rays diffraction investigation indicates that the phosphate-manganate solid solution is complete, at least for this composition range, and follows Vegard's law, while diffuse reflectance and fluorescence spectra confirm that Mn(V) substitutes for P(V) in the barium apatite lattice. EXAFS experiment, at the manganese K edge, performed on the x = 0.2 compound, indicates that the Mn(V)-O distance is 1.73 Å, a much larger value than the P-O distance equal to 1.54 Å.

The (MnO₄)³⁻ vibrational mode frequencies, deduced from the IR and Raman spectra are almost independent of the x value. This indicates that, even at very low manganese content (x = 0.001), the Mn-O distance is also very close to 1.73 Å.

The Mn(V) ion distorts the barium apatite lattice to a large extent when it substitutes for P(V) and imposes its own size to the host sites.

In order to determinate the best crystal growth conditions for KY(WO₄)₂ single-crystals, the investigation of the K₂O-Y₂O₃-WO₃ ternary system was undertaken by the study of three isoplethic sections (K₂W₄O₁₃-Y₂O₃, K₂WO₄-KY(WO₄)₂, K₂W₂O₇-KY(WO₄)₂). The stability domain and the crystallisation field of the compound were then defined: KY(WO₄)₂ is not stoichiometric and melts congruently for the composition 0.81(K₂O.4WO₃)−0.19Y₂O₃ The low temperature phase belongs to the monoclinic system (s.g. C2/c) with a=10.65(1)Å, b=10.34(1)Å, c=7.54(1)Å, β=130.5(1)°. Its crystallisation field was delimited in temperature and composition: an α-KY(WO₄)₂ crystal can grow if x_Y2O3≤0.175.

Synthetic conditions of various zeolites have been investigated starting from coal-mine wastes. Inorganic (NaOH, KOH) or organic (TMAOH, TPAOH, quinuclidine) bases have been used as reacting solution resulting in the preparation of more than ten zeolites with different structural types: MFI, LTL, ERI-OFF, CHA, MER, GIS, ANA, CAN, SOD. The use of a ring separator in the teflon reactor allows to prepare well crystallized impurity-free zeolites.

Single crystals of NaNb₄O₉AsO₄, were prepared, by solid state reaction at 875°C from a mixture of NaNO₃, Nb₂O₅ and NH₄H₂AsO₄. NaNb₄O₉AsO₄ crystallizes in the orthorhombic system, space group Pnma, Z=4, with a=9.9858(7) Å, b=10.3811(6) Å, c=10.4107(6) Å. The diffraction intensities were collected on a Siemens P4 diffractometer with MoKα radiation. The crystal structure was determined and refined from 3465 independent reflections. The three-dimensional framework consists of infinite chains (-NbO₆-NbO₆-AsO₄-)_n, parallel to the b axis and crosslinked via corner sharing by pairs of edge-sharing octahedra. Each pair links four chains. The Na ion partially occupies several independent close positions, with various occupancies, in the interconnected cavities delimited by the framework.

Glass formation is investigated in mixed-halide systems based on CdF₂, NaF, BaF₂, ZnF₂, and CdCl₂. The compositions are optimized for the best compromise between glass stability and low sensitivity to hydrolysis. Addition of 1 mol % rare-earth fluoride does not affect significantly the glass stability. The multiphonon edge is found to depend directly on the chlorine content. Located beyond 9 μm, the position of the IR edge is indicative of low phonon-energy, as compared to pure fluorides. Fundamental vibrations of the host are obtained by means of Raman and far-IR transmission spectroscopies.

The new ultraphosphates FeP₄O₁₁, ZnP₄O₁₁ and CdP₄O₁₁ of the CuP₄O₁₁ structure type were synthesized from the corresponding meta- or polyphosphates and P₄O₁₁. Crystallization via the gas phase has been achieved at elevated temperatures using a mixture of P (3 mg) and I₂ (50 mg) as mineralizer. The crystal structure consists of a two-dimensional phosphate network, built from four crystallographically independent 10-membered polyphosphate rings. Each ring contains four secondary and six tertiary PO₄-groups. Two crystallographically independent metal sites showing sixfold coordination by terminal oxygen atoms are located inbetween the phosphate layers. FeO₆-octahedra (2.028(3) Å < d̄ FeO₆ < 2.268(3) Å) and ZnO₆ octahedra (2.002(2) Å < d̄ ZnO₆ < 2.256(2) Å) exhibit slightly larger radial distortion than the CdO₆-octahedra (2.215(7) Å < d̄ CdO₆ < 2.383(3) Å).

The structure of AlVMoO₇ was solved by direct methods from high resolution X-ray powder diffraction data and refined by the Rietveld method. The lattice constants are a=5.3763(3)Å, b=8.1644(3)Å and c=12.7312Å. Space group Pmcn followed from the systematic extinctions and was confirmed by the successful structure solution. Aluminum is octahedrally coordinated by oxygen, whereas vanadium possesses a distorted pyramidal coordination and molybdenum is tetrahedrally coordinated by oxygen atoms. A three dimensional framework structure results from corner and edge connection of the coordination polyhedra. VO₅ pyramids are edge linked to infinite (VO₂⁺)_∞ chains. Therefore, AlVMoO₇ can be classified as a polyvanadate.